The invention relates to use of microparticles which are microcapsules containing a gas or volatile organic fluid, to obtain images in a Doppler-type ultrasonic mode (sonography) in diagnostic processes, as well as to processes for preparation of such microcapsules.
Various ultrasonic imaging techniques, scanners and imaging modes are known, some of which have different objectives. For example, the echo cardiographic techniques described by Hilman (CA 1,232,837) are said to provide a 2-D echo image or an M-mode echo image of how blood marked by a contrast agent travels through the heart. Tickner et al. (U.S. Pat. No. 4,276,885) indicate that detecting the Doppler shift frequency from the backscatter of bubbles provides a velocity profile for measurement of cardiac output. Doppler modes for ultrasonic imaging include CW Doppler, PW Doppler and color Doppler techniques. Doppler techniques based on signals from ultrasound reflective bodies heretofore have required flowing bodies whose motion forms the basis for the Doppler effect. These quantify the rate and flow direction of moving structures, generally blood flows, by the Doppler shift caused by the red blood cells flowing through the ultrasonic field. See:
1. Omoto, R., Yokote, Y. Takamoto, S., et al: The development of real time two dimensional Doppler echo-cardiography and its clinical significance in acquired valvular disease with special reference to the evaluation of valvular regurgitation. Jpn Heart J 25:325-340, 1984; PA1 2. Bommer, W. J., Miller, L.: Real time two dimensional color flow Doppler: Enhanced Doppler flow imaging in the diagnosis of cardiovascular disease. Am. J. Cardiol. 49:944, 1982 (abstr.); PA1 3. Miyatake, K., Okamoto, M., Kinoshita, N., et al: clinical application of a new type of real-time two dimensional Doppler flow imaging system, Am. J. Cardiol. 54:857-868, 1984; and PA1 4. Omoto, R. (1987) Real time two-dimensional Doppler echocardiography. 2nd Ed., Lea & Febiger, Philadelphia; for details of prior art color Doppler procedures where different Doppler frequencies are displayed as different colors.
On the other hand, it is known that cardial echo contrasts can be achieved through peripheral injection of solutions which contain fine gas bubbles (Roelandt, J., Ultrasound Med. Biol. 8:471-492, 1982). See also Gramiak, Invest. Radiol 3 (1968) 356/366. These gas bubbles are obtained in physiologically compatible solutions, e.g., through shaking, other agitation or through the addition of carbon dioxide. See EP 77,752 and Roelandt, supra. In addition, there are ultrasonic contrast agents in the form of particles (Ophir, Gobuty, McWhirt, Maklad, Ultrasonic Backscatter from Contrast-producing Collagen Microspheres, Ultrasonic Imaging 2:66-67 (1980)). Furthermore, solutions of a higher density are used as ultrasonic contrast agents (Ophir, McWhirt, Maklad, Aqueous Solutions as Potential Ultrasonic Contrast Agents, Ultrasonic Imaging 1:265-279 (1979), as well as Tyler, Ophir, Maklad, In-vivo Enhancement of Ultrasonic Image Luminance by Aqueous Solutions with High Speed of Sound, Ultrasonic Imaging 3:323-329 (1981)). It is also known to use emulsions as ultrasonic contrast agents (Mattrey, Andre, Ultrasonic Enhancement of Myocardial Infarction with Perfluorocarbon Compounds in Dogs, Am. J. Cardiol. 54:206-210 (1984)). Other known contrast agents include the gas bubbles of EP A 2 123 235 and 0 122 624, which correspond to CA 1,232,837 and CA 1,239,092, the gas-filled gelatine or albumin hollow bodies of U.S. Pat. No. 4,774,958 (Feinstein), which corresponds to EP A2 0 224 934, and the microbubbles (gas encapsulated in gelatins of U.S. Pat. No. 4,276,885 (Tickner et al.). All these agents are generally useful in one or more of the known ultrasound imaging modalities, e.g., M-mode, B-mode, various Doppler forms known or published, etc.
In EP 0 052 575, gas bubbles are produced by a solid crystalline substance, such as, for example, galactose, being suspended in a carrier liquid. The gas bubbles originate in this case from gas enclosed in cavities or from gas adsorbed on the crystal surfaces. EP 0 122 624 describes a similar contrast medium based on a non-surface-active substance, such as, e.g., galactose, to which a surface-active substance, such as, e.g., magnesium stearate is admixed, which results in a stabilization of the gas bubbles. Thus, the contrasting of the left side of the heart, as well as of various organs, such as liver, spleen and kidney, was also possible in the 2D-echo image or in the M-mode echo image. DE 38 63 972 discloses gas-filled or liquid-filled microcapsules based on biodegradable polymers, such as, e.g., polycyanoacrylates or .alpha.-, .beta.-, .gamma.-hydroxycarboxylic acids. Similar microcapsules are described in European patent application EP 0 441 468. In contrast to the particles disclosed in DE 38 03 972, the particle shell in this case consists of polyaldehydes. EP 0 224 934 and U.S. Pat. No. 4,276,885 describe gas-filled microcapsules based on proteins or albumins (EP) or based on gelatin (US). The particles of DE 38 03 972 and EP 0 441 468 have in common that they are sufficiently stable and sufficiently small (&lt;10 .mu.m) to pass through capillaries and to be taken up intracellularly in the reticulo-endothelial system (such as, e.g., liver, lymphatic nodes and spleen). But the contrasting in using the B-mode or M-mode technique is not in all cases satisfactory, e.g., differentiating healthy tissue (e.g., liver, spleen, lymphatic nodes) from tumor tissue, which contains only few cells belonging to the reticulo-endothelial system, is often not possible. In addition, the representation of the gastrointestinal tract as well as the perfusion of the myocardium causes difficulties.
Thus, the methods for utilizing these contrast agents have not always provided sufficient signal intensity to represent organs, particularly non-cardiac organs. Quantification of selective concentrations of these contrast agents within organs has not been possible. Particularly in the Doppler techniques, it has been necessary heretofore to utilize contrast giving agents (e.g., the mentioned ultrasound contrast agents) in motion (e.g., perfusion) as a source of the Doppler-based imaging.